Recording pickup having torsion rods



Feb. 27, 1951 BALMER ET AL 2,543,655

RECORDING PICKUP HAVING TORSION RODS Filed March 11, 1947 2 Sheets-Sheet 1 r m Q INVENTORS DONALD F. BALMER FRANK E. RUNGE ATTORNEY Feb. 27, 1951 D. F. BALMER ET AL 2,543,655

RECORDING PICKUPHAVING TORSION RODS Filed March 11, 1947 2 Sheets-Sheet 2 lllir W INVENTORS FRANK E. RUNGE.

ATTORN EY DONALD F. BALMER Patented Feb. 27, 1951 UNITED STATES PATENT OFF-ICE Donald }F. Balmer, New Haven, and Frank E. Runge, .Branf'ord, Conn, assignors to The Soundscriber Corporation, New Haven, 001111., a corporation of Connecticut Application March 11. 1947, SerialNo. 733,744

8 Claims. 1

This invention relates to improvements in phonographic recording apparatus, and more particularly to an improved electromagnetic sound recording head in which a stylus-carrying armature is pivotally mounted within a fixed magnetic field and is energized electrically by a surrounding coil in accordance with the sound vibrations to be recorded.

The present invention is an improvement over that disclosed in the prior Patent "No. 2,222,342, issued November 19, 1940 to Lincoln Thompson, entitled Electromagnetic Sound Recorder, and a prior application to Lincoln Thompson entitled Phonographic Recording Head filed December 7, 1945, Serial Number 637,376.

One object of the present invention is to provide a recording head of the above nature having a relatively small-sized light weight onepiece armature pivoted "on a horizontal axis within a magnetic field, and in which the top of said armature is quite thin and is located in a smaller air gap than the bottom of said armature so that a stronger permanent magnetic flux will be produced. at the top than at the bottom thereof.

A further object is to provide a sound recording head of the above nature, in which the armature is provided with a pair of integral outwardly-extending resilient torsion rods having a pair of integral end blocks which are rigidly soldered between the :faces of the magnet pole pieces and are spaced centrally therebe'tween by a pair of non-magnetic .u..-shaped shims.

A further object is to provide a sound recording head of the above nature having a .pair of yield able side bearing disks for supporting said head on its center of gravity between the sides of a forked recording arm.

A further object is to provide an improved electromagnetic sound recording 'head of the above nature, which will be relatively-simple in construction, inexpensive .to manufacture, compact, ornamental in appearance, and very em cient and durable in use.

With these and other objects in view, which will appear as the description proceeds, there has been illustrated on the accompanying drawing one formin which the-invention may oonveniently be embodied in practice.

In the drawings,

Fig. 1 represents a side vertical view, partly in section, of the sound recording ahead, as it ap pears when resting upon a 'thin disk record, and pivotally mounted in a-recording arm.

Fig. 2 is a longitudinal sectional view, shown on a larger scale, of the recording head with the cording head shown in section.

Fig. 4 is a longitudinal sectional view of the same, taken along the line 44 of Fig. 3,.

Fig. 5 is a transverse sectional view, taken along the line ,55 of Fig. 3.

Fig. 6 is a transverse sectional view, taken along the 'line 66 of Fig. 3.

Fig. '7 is a fragmentary top view of the armature with the upper portion thereof shown in section, and illustrating how said armature is mounted.

Fig. 8 is a perspective View of the armature and spacing shims.

Referring now to the drawings in whi h like reference characters denote corresponding parts throughout the several views, the numeral H] indicates a flat non-magnetic base having a depressed-circular seat 12, near its forward end, which seat is provided with a round hole I I. The seat I2 is adapted to receive a yieldable apertured damping member 13. I r

The base I 0 ,is provided with a hollow top cover casing M having a semi-circular forward section Ma, and a horizontal stop finger l4b on .the rear thereof. The cover casing I4 is adapted to be connected to the base II] by means of a pair of vertical headed holding screws 1 5, 15.

The recording head is mounted at its center of gravity within the sides I8, l9 of a yoke on the front end of a recording arm I! which has a rear depending shoulder 11b for engagement with the stop finger Mb previously mentioned. The sides l8, 19 of the yoke are adapted to support a pair of horizontal pivot pins 20, 2! having conical inner ends 20a, Zia, which are adapted to engage a pair of flexible spring meta1 diaphragm disks 22, 23 seated at their outer peripheries in the opposite vertical sides of the cover l4 and being unsupported at their central sections.

The pivot pins 2!), 2 I are secured in adjusted position :by means of a pair of lock nuts 24, 25 screwed upon threaded outer sections 26, 21 of said pins.

In order to provide a permanent magnetic field for a vertical armature 34, provision is made of a pair :of :L -shaped magnetic pole pieces 28, 29 rigidly secured in abutment with the sides of a rectangu'larrear magnetic block 30, by means of a pair of horizontal clamping screws 3|, 32, located at the front and rear of said magnetic block, respectively.

The pole pieces 28, 29 are adapted to embrace a cylindrical ring-shaped coil 33 mounted on a vertical axis, and held rigidly in operating position by means of a pair of inwardly-extending U-shaped side sections 33a, 33b integral with the forward portions of said pole pieces.

The armature 34 is mounted to vibrate on a horizontal axis and has a socket section 36 at the bottom thereof for receiving an angular stylus-holding rod 36a. The socket section 35 is tightly embraced by the damping block l3, and the rod 36a has a diamond-tipped stylus S at the lower forwardly-inclined end thereof. The armature 34 is also provided with a wide fiat top thin portion 35, which is adapted to be located in a small air gap between the closely spaced sections 33a, 33b of the pole pieces 28, 29. The armature 34 is also provided with a pair of integral opposed torsion rods 31, 38 extending longitudinally from an intermediate block 34a, and having integral end blocks 39, 40 which are rigidly soldered between the lower inwardly-extending arms of the U-shaped side sections 33a and 33b of the pole pieces 28, 29. The intermediate rectangular block 34a is located in a relativelv wide air gap at the bottom of the U-shaped side sections 33a, 33b of the pole pieces 28, 29, as shown in Fig. '7.

Provision is also made of a pair of vertical headed attaching screws 4|, 42 for holding the bottom of the base I 9 upon the U-shaped depending sections 33a, 33b of the pole pieces 28. 29.

In order to centralize the blocks 39, 49 accurately between the pole pieces, provision is made of a pair of inverted U-shaped non-magnetic guide shims 43, 44 embracing said blocks 39. 40 and embedded in the solder which joins said blocks to the pole pieces 28, 29.

The coil 33 is adapted to be connected to the amplifier of a photographic dictating machine, not shown, by means of a pair of lead wires 45, 46 which are received within a longitudinal groove 41 in the rear of the base In.

Operation In operation, a flux of steady permanent magnetic lines of force will pass across the upper and lower gaps of the magnet between the forward ends of the pole pieces 28, 29, and through the armature 34-the magnetic circuit being completed through the rear magnet block 30. The stylus 34a will be caused to vibrate laterally to produce an undulating spiral groove in a record R mounted on a turntable T in accordance with the electrical oscillations received in the coil 33 which is energized by the recorder amplifier.

While there has been disclosed in this specification one form in which the invention may be embodied, it is to be understood that this form is shown for the purpose of illustration only, and that the invention is not to be limited to the specific disclosure, but may be modified and embodied in various other forms without departing from its spirit. In short, the invention includes all the modifications and embodiments coming within the scope of the following claims.

Having thus fully described the invention, what is claimed as new, and for which it is desired to secure Letters Patent, is:

1. In a phonographic sound recording head, a magnet having a pair of L-shaped pole pieces comprising forward spaced centrally recessed inwardly extending side sections, said side sections having upper and lower pairs of opposed end faces above and below the recesses defining upper and lower air gaps, a stylus-holding armature located between said pole pieces, an armature-actuating coil disposed in the recesses of said pole pieces and embracing said armature, said armature having a pair of resilient oppositely extending torsion rods disposed between said pole pieces below said recesses and each comprising an integral end portion rigidly and directly attached to said lower pair of end faces.

2. The invention defined in claim 1, in combination with a recording arm, said recording head being embraced by a cover casing secured thereon, and having a pair of opposed spring metal disks supported at their peripheries in the sides of said cover casing,said disks being disposed on a transverse axis passing through the center of gravity of said head, said recording arm being provided with a pair Of conically shaped inwardly-extending pivot pins for engaging said disks for resiliently pivotally mounting said head on said arm.

3. Theinvention defined in claim 1, in which said upper air gap is small in relation to said lower air gap, said upper and lower gaps embracing upper and intermediate sections of said armature, respectively 4. The invention defined in .claim 1, in which said recording head is provided with a flat base, and has a hollow cover casing secured thereto for embracing said magnet and said armature, said recording head being pivotally mounted in a recording arm having a depending portion, said casing having a rearwardly-extending stop finger for engaging said depending portion.

5. The invention defined in claim 1, in combination with a recording arm, said recording head being embraced by a cover casing secured thereon and having a pair of opposed resilient yieldable members disposed on a transverse axis passing through the center of gravity of said head, said recording arm being provided with a pair of conically-shaped inwardly-extending pivot pins engaging said members for pivotally mounting said head on said arm.

6. The invention as defined in claim 1, in which said end portions of said torsion rods comprise blocks fitted between and soldered to said pole pieces.

7. In a phonographic sound recording head, a magnet having a pair of L-shaped pole pieces comprising forward spaced centrally-recessed inwardly extending side sections providing upper and lower air gaps, a stylus-holding armature located between said pole pieces, an armatureactuating coil disposed in the recesses of said pole pieces and embracing said armature, said armature having a pair of resilient oppositely extending torsion rods disposed between said pole pieces below said recesses, the outer ends of said torsion rods comprising blocks fitted between and soldered rigidly to said pole pieces, each 0f said blocks being centralized between said pole pieces by an inverted U-shaped shim membe embracing said blocks, said shim member being shorter than said block.

8. In a phonographic sound recording head, a magnet having a pair of L-shaped pole pieces comprising forward spaced centrally recessed inwardly extending side sections providing upper and lower air gaps, a stylus-holding armature located between said pole pieces, and an armatureactuating coil disposed in the recesses of said pole pieces and embracing said armature, said armature having a pair of resilient oppositely extending torsion rods disposed between said pole pieces below said recesses, said torsion rods being integrally provided with blocks soldered rigidly to said pole pieces, and shims which embrace said blocks to centralize said blocks between said pole pieces.

DONALD F. BALMER. FRANK E. RUNGE.

REFERENCES CITED 9 The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS Number Name Date Ray Oct. 14, 1930 15 Number 

